1. Field of the Invention
The invention is related to an internal combustion engine capable of reforming and recycling a portion of fuel included in exhaust gas from a combustion chamber.
2. Description of the Related Art
There are known internal combustion engines that are provided with a reformer (catalyst device) within an exhaust passage, which includes a passage in which exhaust gas flows and a reforming catalyst disposed so as to be heated by exhaust gas flowing through the passage (refer to Japanese Patent Publication No. 60-37310 and Japanese Patent Publication No. 61-35375 for examples). In this type of internal combustion engine, fuel is mixed into a portion of exhaust gas taken from the exhaust passage downstream from the reformer. The mixture is delivered into the reforming catalyst which is heated using heat of exhaust gas in the aforementioned passage. Moreover, an endothermic reforming reaction using heat from the exhaust gas is advanced in the reforming catalyst to create a reformed fuel including hydrogen and carbon monoxide. The reformed fuel obtained is then supplied as fuel to an air intake system and reused.
In addition, there is also a known natural gas reforming engine system that reforms reforming source gas such as natural gas and supplies the reformed gas to the engine, and uses a portion of exhaust gas as additive gas for reforming source gas (refer to Japanese Patent Laid-Open Publication No. 2002-98010 for an example). In such an engine system, a heat exchanger for heating source gas and a gas reformer are disposed in this order from the upstream side of a fuel supply passage that connects a source gas supply and the engine. Furthermore, the gas reformer is provided in an exhaust passage of the engine in order to use heat of engine exhaust gas as a heat source. Therefore, a portion of exhaust gas is taken from the exhaust passage downstream from the gas reformer in this system, and this exhaust gas is mixed into source gas via an exhaust branch passage.
However, in internal combustion engines such as described above, exhaust gas to be mixed with fuel or source gas is taken from the vicinity of the farthest downstream portion of the exhaust passage. Thus, when the amount of residual fuel in the exhaust gas is increased in order to increase the amount of fuel fed to the gas reformer, this leads to a corresponding increase in the amount of unreformed fuel released to the atmosphere.